1. Field of the Invention
This invention relates to a ceramic heating element comprising a ceramic substrate having on a surface thereof a resistor pattern made of an inorganic electrically conductive material and a ceramic electrically insulating layer disposed on the surface of the ceramic substrate having the resistor pattern thereon. More particularly, it relates to a ceramic heating element whose resistivity can be adjusted to a certain value.
2. Description of the Prior Art
A ceramic heating element comprising a ceramic substrate having formed thereon a resistor pattern made of an inorganic electrically conductive material and coated with a ceramic electrically insulating layer is conventionally known. Such a heating element is produced by first coating or metalizing a resistive paste that contains an inorganic electrically conductive material onto a ceramic green sheet, superimposing another ceramic green sheet on the first ceramic green sheet to form an integral element, and calcining the integral element. However, in this conventional method, the resistivity of the resulting resistor varies so greatly, depending on factors such as the metalizing width and thickness as well as the calcining conditions, that it is extremely difficult to obtain a desired constant resistivity value or resistivity within a certain range, and therefore, a ceramic heating element of high quality cannot be produced efficiently on a commercial scale.
British Pat. No. 1,236,580 discloses a thin film electrical-resistor comprising an electrically insulating thin synthetic resin film as a substrate. Of course, the procedures described therein cannot be used for producing ceramic heating elements because of the nature of the synthetic resin thin film used as a substrate.